The present invention relates to contact elements for establishing an electrical contact in that, when the contact elements are joined, a contact element cuts into or pierces an electrical conductor.
Plug-type connections generally are disengageable or non-disengageable electrical connections of one or more contacts, electrical contact being established by inserting complementary contact elements, such as a plug and a socket, one into the other.
In the case of disengageable contacting a connection is regularly established in that one contact element bears resiliently against the other element or is clamped onto the other element. In this respect there are many alternatives such as, for example sockets and resilient pins, resilient sockets and pins, leaf springs on pads, shear clamps, wire clamps, pin clamps, screw-type clamps for wires or pins and so on. Plug-type connections of this kind are customarily provided for numerous insertion and withdrawal cycles.
As opposed to the disengageable electrical connections, in the case of non-disengageable electrical connections an electrical contact is to be established that is regularly only a one-time, non-disengageable electrical connection. Among the non-disengageable electrical connections there are notably the piercing clamping connections where a one-time contact is established through an insulated cable by means of a piercing element. Contacting normally takes place in the direction perpendicular to the sheath of the electrical conductors.
Finally, in addition to the disengageable or non-disengageable electrical connections in the strict sense of the word there are also hybrid forms that are designed for more or less numerous insertion and withdrawal cycles, for example, piercing clamping connections that are intended for a given number of insertion and withdrawal cycles. Piercing clamping connections of this kind are described inter alia in EP-A-131705 or WO 98/29031.
Nowadays a typical example of a disengageable electrical connection is encountered in the medical field for the purpose of birth monitoring, that is, for the so-called fetal galea or scalp electrodes for monitoring the fetal cardiac activity. The fetal scalp electrode is used to record the ECG of the unborn child by means of two electrodes. At the side of the scalp electrodes there are provided two open (bared) tinned wires for contacting two resilient jaws as counter contacts at the apparatus side. Applicant discloses fetal scalp electrodes of this kind inter alia in U.S. Pat. No. 5,423,314 or U.S. Pat. No. 3,750,650.
The fetal scalp electrode customarily is a disposable product; therefore, like other medical disposable articles it should be as inexpensive as possible. The simple bare contact wires satisfy this cost requirement.
International regulations, such as imposed by the FDA (Food and Drug Administration) or MDD (Medical Device Directive), stipulate that the open, electrically conductive wires of the fetal scalp electrodes must be replaced by an insulated plug-type connector so as to protect the patients against incorrect contacting.
A further requirement that is imposed in particular on fetal scalp electrodes is that the plug element should be as small as possible, because must be easy to pull this element through an inner tube of an introduction instrument in the known embodiments.
A plug-type connection of this kind for fetal scalp electrodes that notably satisfies said safety regulations is known from EP-A-484107. According to that plug-type connection system the two wires are connected to insulated sockets (in conformity with the known jack plug connection), said sockets subsequently being placed on pins. This arrangement, however, has the drawback that, because of the necessary limitation of the dimensions of the plug element, its manufacture is intricate and hence expensive.
Therefore, it is an object of the present invention to provide a method of electrical contacting that on the one hand enables the use of insulated plug-type elements, for example, in order to satisfy said safety regulations, and on the other hand enables plug elements to be proportioned so as to be as small as possible. The method of contacting in accordance with the invention should also enable the manufacture of as inexpensive as possible plug-type contacts that are notably suitable for medical disposable articles such as, for example fetal scalp electrodes. This object is achieved as disclosed in the characterizing part of the independent claims. Advantageous embodiments are disclosed in the dependent claims.
The invention is based on the idea to design the plug element of a clamping piercing connection that consists of a plug and a socket to be such that the plug element is enclosed by a molding, prior to the establishment of an electrical contact, in such a manner that electrical conductors of the plug (at least those that are to be contacted) are completely electrically insulated at the contact side. Electrical contact is then established by the piercing of or cutting into the corresponding electrical conductors of the plug by contact elements. The molding may be designed so as to be connected to and integral with the plug conductors or as separate parts, and is preferably essentially complementary to a corresponding recess in the socket in which the plug is to be inserted for the purpose of contacting. Depending on the relevant design, the plug can be introduced into the socket in the pulling direction of the plug conductors, in the direction perpendicular thereto or at an arbitrary angle; pull-out forces for separating the connection and/or for pulling out the cables can be defined and determined by suitable design.
According to the known clamping piercing connections (see notably the cited EP-A-131705 or WO 98/29031), usually only the cables that are insulated by way of the cable insulation are pierced by appropriate knives and the end of the electrical conductors at the contact side, which is usually only cut off, can thus give rise to undesirable electrical contacts. In contrast therewith, however, the molding in accordance with the invention also provides electrical insulation for the end of the electrical conductors at the contact side, thus enabling undesirable electrical contacts to be avoided.
Because of the essentially complementary design of the molding and the corresponding socket recess, moreover, the clamping piercing operation can be specified and concretized in defined insertion positions. Furthermore, suitable codes and/or locking mechanisms can be used in conformity with the relevant application.
The solution in accordance with the invention is particularly suitable to enable the safety contacting necessary for fetal scalp electrodes. However, the solution in accordance with the invention is not restricted to medical applications in general or to fetal scalp electrodes in particular, but is suitable for all disengageable plug-type connections where only a small number of insertion and withdrawal cycles is required at the plug side. This concerns notably disposable articles or other applications where it is necessary to establish a disengageable contact which, however, as a rule is closed or opened only once or a few times.
When the solution in accordance with the invention is used, notably in the case of fetal scalp electrodes, it is ensured that the safety regulations can be met at low costs. Moreover, the electrical connection operation is significantly simplified for the user. Because the user normally wears protective gloves and such gloves are moist because of the vaginal introduction of the fetal scalp electrode, it is not easy to control the customarily used spring jaws and the insertion of the bared wires. This situation is significantly improved by means of a plug-type connection in accordance with the invention, because the user can reliably control the plug with one hand only.
Depending on the relevant field of application, the solution in accordance with the invention enables low-cost manufacture of the plug contacts that are to be used for small numbers of insertion and withdrawal cycles. The invention notably enables very inexpensive manufacture of only a part of the plug-type connection, that is, preferably the insulated plug element. The second part of the plug-type connection can then be manufactured at costs that correspond to those of the solutions used at present (for example, the costs of tinning the bared wires correspond to the costs of molding a plug in accordance with the invention around the cable). This means that the advantage of the basic idea of the solution in accordance with the invention may reside notably in the costs of such plug-type connections where, for example, the costs of the plug should be low and the plug is required for a small number of insertion and withdrawal cycles only. The invention is thus particularly suitable for disposable articles of the kind frequently used for reasons of hygiene in the medical field.
A preferred embodiment of a plug-type connection in accordance with the invention is provided on the one side (at the cable side) with a plug element that is arranged on a cable (preferably not bared) and is preferably molded on the cable while using a synthetic material, and on the other side (the side to be contacted) with a socket element for receiving the plug element. A suitable bond can be realized between the plug element and the cable insulation notably when the same synthetic material is used for the plug element and for the cable insulation. The plug element at the side of the cable is formed in such a manner that it can be preferably inserted into the opening of the socket element so as to be locked against rotation. During the insertion operation a piercing contact member that projects into an open space of the socket element pierces the cable conductor through the insulation and hence establishes an electrical connection between a contact element of the socket element and the cable conductor. Similarly, in the case of a plurality of cable conductors a plurality of piercing contact members may be provided, each of said members establishing a respective electrical connection between a corresponding contact element of the socket element and the relevant cable conductor.
The socket element in a preferred embodiment is formed as a removable or exchangeable element so as to enable a fast exchange of the socket, for example, in the case of deterioration of the piercing intensity or for the purpose of cleaning or sterilization of the socket element. In conformity with the relevant application, the socket element may also be constructed as a disposable product.
The socket element in another embodiment can be connected in a plug-type fashion to a connection element, for example, to a measuring apparatus or a leg plate (in the case of the fetal scalp electrode) so as to ensure a fast and simple exchange. A possibly specified pull-out force can then be realized by way of an appropriate design and/or proportioning of this plug-type connection; the socket element then becomes disengaged from the connection element under the influence of pulling. This may be necessary or desirable notably in the case of medical applications such as the fetal scalp electrode.
The plug is preferably designed in such a manner that it still has an electrically insulating effect even after execution of a number of piercing clamping operations, be it in some cases to a limited extent only. This effect can be achieved, for example, by way of a suitable choice of the materials and/or dimensions of the cable insulation and/or the molding, so that, for example, the cable insulation and/or the molding return to their initial position (prior to the establishment of the piercing clamping connection) to a given degree after the disengaging of the clamping piercing connection. Furthermore, the risk of undesirable electrical contacts after the disengaging of the piercing clamping connection can be mitigated by providing suitable air gaps.